Phacoemulsification machine with post-occlusion surge control system and related method

ABSTRACT

A post-occlusion surge controller  90  for a phacoemulsification machine  30  is adapted to detect a post-occlusion surge in an aspiration conduit  41  of the machine  30 , and to cause the conduit  41  to be vented in response to detecting the surge.

FIELD OF THE INVENTION

The present invention relates generally to phacoemulsification machineswhich are used in cataract eye surgery to remove cataract-affected eyelenses and, in particular, to phacoemulsification machines which areadapted to control post-occlusion surges which sometimes occur duringcataract eye surgery when such machines are used.

Although the invention will be described with reference to a particulartype of phacoemulsification machine, it will be appreciated that this isby way of example only and that the invention may be used in connectionwith other types of phacoemulsification machines.

BRIEF DISCUSSION OF THE PRIOR ART

Phacoemulsification or phaco-machines are used in cataract eye surgeryto remove cataract-affected eye lenses. FIG. 1 depicts a typical priorart peristaltic pump-based phaco-machine 30 which includes a hand-heldprobe 31 comprising a hollow infusion sleeve 32 surrounding a hollowphacoemulsification needle 33. Needle 33 projects from an end of theinfusion sleeve 32 and is vibrated at ultrasonic frequencies byultrasonic crystals 34 which reside inside the probe 31 and which areconnected to a controller 35 which is operable to cause the ultrasoniccrystals 34 to vibrate. The sleeve 32 of probe 31 is connected to anelevated and inverted bottle 36 which contains an infusion fluid 37 by acompliant infusion tube 38. The needle 33 is connected to an input port39 of a peristaltic pump 40 by a length of aspiration tube 41.

The peristaltic pump 40 includes a rotatable rotor 42 which has aplurality of circumferentially-spaced rollers 43 secured thereto and isdriven by a motor. A compliant pump tube 44 which is connected to theaspiration tube 41 extends around the circumference of the rotor 42 andis located between the rotor 42 and an arcuate wall 45 of the pump 40such that the rollers 43 which are in contact with the tube 44 pinch thetube 44 between themselves and the wall 45. As the rotor 42 rotatesabout its axis, each of the rollers 43 progresses along the wall 45 sothat the pinches in the tube 44 also progress along the wall 45. Therotor 42 rotates in a clockwise direction so that fluid is drawn throughthe tube 44 from the input port 39 of the pump 40 and is output from anoutput port 46 of the pump 40 into a collection bag 47.

The machine 30 also has a vacuum sensor 48 for sensing the vacuum whichis produced inside the aspiration and pump tubes 41, 44 by theperistaltic pump 40. Vacuum sensor 48 is connected to the controller 35.

A compliant venting tube 49 interconnects the input and output ports 39,46 of the pump 40, and a vent pinch valve 50 is operable by thecontroller 35 to selectively pinch the venting tube 49. When the ventingtube 49 is released by the valve 50, the lumen of the aspiration andpump tubes 41, 44 are connected to atmospheric pressure by the ventingtube 49.

Although the phaco-machine 30 vents to the output 46 of the pump 40,other phaco-machines may vent to air, the infusion bottle 36 or to acassette system.

An infusion pinch valve 51 is operable by the controller 35 toselectively pinch the infusion tube 38 to prevent the infusion fluid 37from flowing from the bottle 36 to the sleeve 32.

The operation of the peristaltic pump 40 is controlled by afoot-operated pedal 52 which is coupled to the controller 35. Depressingthe pedal 52 by one-third causes the rotor 42 of the pump 40 to commencerotating. Further depression of the pedal 52 increases the speed ofrotation of the rotor 42 in proportion to the amount by which the pedal52 is depressed. When the pedal 52 is released the rotor 42 stopsrotating so that the pump 40 stops aspirating. The pedal 52 is also usedto control the vibration of the needle 33 and the infusion pinch valve51 which controls the flow of infusion fluid 37 from the bottle 36through the infusion tube 38 and from the sleeve 32. The needle 33normally begins vibrating when the pedal 52 is depressed by two-thirds.When the pedal 52 is initially depressed, the infusion pinch valve 51releases the infusion tube 38 during the initial one-third of thedepression of the pedal 52 so that the infusion fluid 37 is able to flowfrom the bottle 36 through the infusion tube 38 and from the sleeve 32.The ultrasonic crystals 34 commence vibrating once the pedal 52 isdepressed by more than two-thirds. In addition to stopping the pump 40,releasing the pedal 52 causes the ultrasonic crystals 34 to stopvibrating, and the infusion pinch valve 51 to pinch the infusion tube 38so that the infusion fluid 37 stops flowing from the bottle 36 to theinfusion sleeve 32. Releasing the pedal 52 may also cause the vent pinchvalve 50 to release the venting tube 49 so that the aspiration tube 41is vented to the collection bag 47. In general, the pedal 52 controlsthe three basic functions of fluid irrigation (infusion), aspiration,and vibrating of the needle (phacoemulsification). These functions canbe allocated to any range of pedal depression by the user of the machine30.

In use, the tip of the needle 33 is inserted into the anterior chamberof a patient's eye 53 by an eye surgeon such that the tip of the needle33 is positioned adjacent to the cataract-affected lens in the eye 53which is to be removed using the phaco-machine 30. The surgeon thendepresses the pedal 52 so that the infusion fluid 37 flows from thebottle 36 and into the anterior chamber of the eye 53 from the infusionsleeve 32, and so that the peristaltic pump 40 commences aspirating, andthe ultrasonic crystals 34 commence vibrating the needle 33. As theneedle 33 vibrates at ultrasonic frequencies, the vibration breaks upthe natural cataract-affected lens in the eye 53 and small particles ofthe lens are aspirated through the hollow needle 33 and into theaspiration tube 41 as a result of the vacuum produced within the lumenof the tube 41 by the operation of the pump 40. The particles then flowinto the pump tube 44 from the aspiration tube 41 and then into thecollection bag 47 for disposal. The object of the surgery is to leavethe thin outer capsule of the lens behind to form a home for anartificial plastic lens which is inserted into the eye 53 to replace thecataract-affected lens. Infusion fluid 37 from the bottle 36 flows intothe anterior chamber of the eye 53 from the sleeve 32 so as to maintainvolume and pressure in the anterior chamber and to prevent the chamberfrom collapsing while the pump 40 is operating.

The vacuum sensor 48 of the machine 30 enables the controller 35 tocontinuously monitor the vacuum inside the aspiration tube 41 at alocation which is adjacent to the input port 39 of the peristaltic pump40. If the controller 35 determines that the vacuum inside the tube 41has reached a predetermined maximum allowable level, such as a 300 to500 mmHg vacuum, the controller 35 causes the peristaltic pump 40 tostop operating. Vacuums of 300 to 500 mmHg are usually only generatedwhen the tip of the needle 33 is occluded by particles of the cataractor other tissue. In general, the vacuum in the aspiration tube 41 willnot rise above 150 mmHg without a degree of occlusion as only modestvacuums of 0 to 100 mmHg are required in the un-occluded state tosupport the typically used 20 to 60 ml/minute fluid flow rates throughthe tube 41.

A post-occlusion surge will appear in the aspiration tube 41 if, afterthe vacuum in the aspiration tube 41 has reached the predeterminedmaximum level and the peristaltic pump 40 has stopped aspirating, theocclusion in the tip of the needle 33 suddenly breaks free. Thepost-occlusion surge is a result of the pump tube 44, vacuum sensor 48,and the aspiration tube 41, which are constructed from compliantmaterials, being compressed by atmospheric pressure just prior to thesurge occurring so that they store potential energy. This is depicted inFIG. 2 where the various compliant components of the machine 30 arerepresented by a compliant chamber 54. When the occlusion breaks free,the pump tube 44, vacuum sensor 48, aspiration tube 41, and othercompliant components connected thereto, expand and rapidly draw fluidinto the aspiration tube 41. This causes a sudden rush of fluid from theanterior chamber of the eye 53 and into the needle 33 and aspirationtube 41 as depicted by the arrow 55 so that the compliant chamber 54 andaspiration tube 41 expand as depicted by the arrows 56. This sudden rushof fluid can cause the anterior chamber of the eye 53 to collapse andeye tissue to rush toward the tip of the needle 33. Eye tissue such asthe lens capsule, corneal endothelium (which are important fragile cellson the inner surface of the cornea), or the iris may be engaged by theneedle 33 at the time of the surge so that the surge causes significantdamage to the tissue. The probability of the post-occlusion surgecollapsing the anterior chamber of the eye 53 increases if there isfluid leakage from the anterior chamber around the instruments, probe31, and manipulators which are inserted into the anterior chamber.

Valve 50 of the machine 30 is used for venting purposes and generallypinches the venting tube 49 when the machine 30 is in use so that fluidis unable to flow through the venting tube 49. The vent pinch valve 50may release the venting tube 49 at any time in order to neutralise anyresidual vacuum in the aspiration tube 41. For example, when the pedal52 is released, the vent pinch valve 50 may release the venting tube 49in order to neutralise the vacuum in the aspiration tube 41. The ventpinch valve 50 does not normally release the venting tube 49 during apost-occlusion surge.

FIG. 3 is a typical graph of the variation over time of the pressure inthe aspiration tube 41 at a location therein which is adjacent to thevacuum sensor 48 immediately after an occlusion in the tip of the needle33 breaks free, where the maximum allowable vacuum had been set by theuser at 500 mmHg. It can be seen that the vacuum inside the aspirationtube 41 decreases from −500 mmHg to the positive pressure inside the eye53 (which can be expressed pgh, where p is the density of the infusionfluid 37, g is the acceleration of gravity, and h is the height of thebottle 36 above the eye 53) which is above atmospheric pressure (i.e. 0mmHg), and which is typically 51 mmHg with a 70 centimetre bottle heightsuch that the vacuum halves after approximately 220 milliseconds. Theactual amount of time required to halve the vacuum in the aspirationtube 41 is dependent on the compliance of the materials from which thecompliant components of the machine 30 are fabricated as well as thegeometry of those components.

FIG. 4 is a typical graph of the rate of flow of fluid through theaspiration tube 41 of the phaco-machine 30 immediately after theocclusion in the tip of the needle 33 breaks free. It can be seen thatthe flow of fluid peaks at approximately 100 millilitres per minute, oraround five times the normal flow rate, approximately 220 millisecondsafter the blockage in the needle 33 clears. The flow rate then graduallydecreases to a normal flow rate. The flow peak depends on the vacuum inthe aspiration system immediately prior to the start of thepost-occlusion surge, and also the geometry of the needle 33 of theprobe 31 and aspiration tube 41, and the compliance of the aspirationtube 41, vacuum sensor 48 and peristaltic pump tube 39.

FIG. 5 is a typical graph of the pressure inside the anterior chamber ofthe eye 53 immediately after the occlusion in the needle 33 breaks free.It takes approximately 220 milliseconds for the pressure to decreasefrom the positive pressure of the infusion fluid inside the anteriorchamber of the eye 53 which is proportional to the height of the bottle36, to around zero pressure at which point the anterior chambercollapses. As the flow rate of fluid through the aspiration tube 41decreases, the pressure inside the anterior chamber steadily increasesback to its former pressure. Unless the peristaltic pump 40 re-startsbefore the end of the surge, the pressure in the anterior chamber of theeye 53 will return to a value between pgh (i.e. the bottle pressure) andzero as depicted by the dotted line in FIG. 5.

The peak flow rate and pressure depicted in FIGS. 4 and 5 areproportional to the vacuum inside the compliant structures of themachine 30 just prior to the occlusion in the needle 33 breaking free.This vacuum is normally the maximum allowable vacuum set on the machine30. The profile of the post-occlusion surge flow depicted in FIG. 4, andthe anterior chamber pressure drop depicted in FIG. 5, and the loss ofvacuum in the compliant system depicted in FIG. 3, are able to bedetermined by the mathematics and physics of damped simple harmonicmotion. The stored energy in the compliant structures acts like aspring, this acts on the mass of the fluid being accelerated in theaspiration tube 41, and the resistance in this case is the resistance tofluid flow in the aspiration system. This resistance to fluid flow dampsthe oscillations. The surge flow profile therefore represents a halfcycle of very damped oscillation.

Phaco-machine manufacturers have attempted to reduce the post-occlusionsurge by reducing the compliance of the compliant components by usingnon-compliant aspiration tubing and by improving the flow of infusionfluid from the sleeve 32 and into the eye 53.

Another approach which has been used to reduce the amplitude of thepost-occlusion surge has been to place what amounts to resistance in theaspiration tube 41 or in the tip of the needle 33. This can involveplacing a small aperture in the aspiration tube 41 which fluid flowingthrough the tube 41 must pass through. The aperture may need to befiltered to prevent particles such as cataract particles from blockingthe aperture.

Another technique for increasing the resistance involves decreasing theinternal diameter of the tip of the needle 33 or otherwise modifying theneedle 33 to create more turbulence and therefore resistance to the flowof fluid through the needle 33 and the aspiration tube 41.

Yet another method of increasing the resistance to the flow of fluidthrough the needle 33 and the aspiration tube 41 involves the use oftubing with a spiral lumen. This creates turbulent flow at higher flowrates which helps suppress the amplitude of the post-occlusion surge.

Although increasing the resistance of the aspiration tube 41 or othercomponents of the aspiration system of the machine 30 does reduce theamplitude of the post-occlusion surge, it has the disadvantage ofprolonging the duration of the surge. Adding resistance to theaspiration tube also has the significant disadvantage of reducing theflow rate, especially at vacuums below 150 mmHg. Also, as the probeneedle 33 is cooled by the flow of infusion fluid, adding resistanceresults in an increase in probe temperature which increases thepossibility of the probe needle 33 causing wound burns to the eye 53.Therefore, in the absence of any other means of reducing thepost-occlusion surge, it is usually better to reduce the compliance ofthe compliant components as mentioned earlier rather than to increasethe flow resistance in the aspiration pathways. However, there arelimitations to the amount by which the compliance can be reduced becausethe compliant components of the machine 30 such as the pump tube 44 andthe vacuum sensor 48 need to have some compliance in order for themachine 30 to operate properly. Also, the aspiration tube 41 needs to beflexible enough to handle easily and to be kink resistant, so itinevitably has to have some compliance.

Another known method of reducing the impact of the post-occlusion surgeis to increase the elevation of the bottle 36 relative to the probe 31so as to increase the rate of flow of infusion fluid into the anteriorchamber of the eye 53 from the sleeve 32. However, if the bottle 36 istoo high other problems result. For example, it is not widely known thatincreasing the height of the bottle 36 actually increases the magnitudeof the post occlusion surge, and therefore the anterior chamberdisturbance associated with it. This is because the surge isproportional to the sum of the absolute values of both the bottlepressure and the maximum vacuum prior to the surge. The maximum vacuumis the dominant value, and increasing the bottle height increases theanterior chamber pressure, moving the apex or peak of the surge awayfrom zero pressure and therefore away from total chamber collapse.Therefore, the surgeon using the phaco-machine 30 is given theimpression that the anterior chamber is more stable than it really is,despite the amplitude of the pressure drop of the surge being a littlegreater with the bottle being more elevated.

Although eye surgeons prefer their phaco-machines to have a relativelyhigh predetermined maximum allowable vacuum level so as to improve theirability to efficiently remove lens fragments, they usually mustcompromise this with the maximum post-occlusion surge which they areprepared to tolerate since the post-occlusion surge is directlyproportional to the maximum allowable vacuum level.

It would therefore be beneficial to have a phacoemulsification machinewhich has a relatively high predetermined maximum vacuum level so thatlens fragments can be removed efficiently from the anterior chamber ofan eye which is operated on using the machine, but which has a reducedpost-occlusion surge.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome, or at leastameliorate, one or more of the deficiencies of the prior art mentionedabove, or to provide the consumer with a useful or commercial choice.

Other objects and advantages of the present invention will becomeapparent from the following description, taken in connection with theaccompanying illustrations, wherein, by way of illustration and example,a preferred embodiment of the present invention is disclosed.

According to a first broad aspect of the present invention there isprovided a post-occlusion surge controller for a phacoemulsificationmachine, wherein the controller is adapted to detect a post-occlusionsurge in an aspiration conduit of the machine, and to cause the conduitto be vented in response to detecting the surge.

By detecting the post-occlusion surge in an aspiration conduit of thephacoemulsification machine, and venting the conduit in response todetecting the surge, the post-occlusion surge controller is able tolimit the duration and the amplitude of the post-occlusion surge in theconduit. Limiting the duration and amplitude of the post-occlusion surgereduces the risk of injuring an eye which is being operated on with themachine when the post-occlusion surge occurs.

The post-occlusion surge controller may be adapted to be used with anytype of phacoemulsification machine. For example, the post-occlusionsurge controller may be adapted to be used with a peristaltic pump-basedphacoemulsification machine. In a particular preferred form thepost-occlusion surge controller is adapted to be used with a peristalticpump-based phacoemulsification machine which includes an aspiration tubeconnected to a peristaltic pump, a venting tube connected to theaspiration tube, and a vent pinch valve operable to pinch the ventingtube to prevent venting of the aspiration tube through the venting tube.

Preferably, the post-occlusion surge controller is adapted to detect theonset of the post-occlusion surge, and to cause the conduit to be ventedin response to detecting the onset of the surge. This enables theconduit to be vented early on during the surge so that the amplitude andduration of the surge may be minimised.

The post-occlusion surge controller preferably includes a detector fordetecting the onset of a post-occlusion surge in the aspiration conduitof the phacoemulsification machine, and a valve controller forcontrolling a vent valve of the machine in response to the detectordetecting the onset of the surge.

The detector preferably includes a differentiator for differentiatingthe output of a vacuum sensor of the machine which senses the vacuuminside the aspiration conduit of the machine, and a comparator forcomparing the output of the differentiator with a reference value andfor outputting a trigger signal depending upon the outcome of thecomparison.

The valve controller preferably includes a timer for outputting a ventvalve control signal in response to receiving the trigger signal fromthe detector, and a vent valve driver for driving the vent valve of thephacoemulsification machine to vent the aspiration conduit in responseto the timer outputting the vent valve control signal.

Preferably, the valve controller also includes a high voltage pulsegenerator for outputting a high voltage pulse signal to a solenoid ofthe vent valve in response to the timer outputting the vent valvecontrol signal.

It is also preferred that the valve controller includes a vent valvepre-energiser for pre-energising the solenoid of the vent valve toreduce the time required for the vent valve to respond to the highvoltage pulse signal which is output to the solenoid by the high voltagepulse generator.

According to a second broad aspect of the present invention there isprovided a method of controlling a post-occlusion surge in an aspirationconduit of a phacoemulsification machine, the method comprising thesteps of:

-   -   (i) detecting the post-occlusion surge; and    -   (ii) venting the conduit in response to detecting the surge.

Preferably, the step of detecting the post-occlusion surge involvesdetecting the onset of the surge, and the step of venting the conduit isdone in response to detecting the onset of the surge so that theamplitude and duration of the surge is minimised.

The step of detecting the onset of the surge preferably includesdetermining whether the negative of the rate of change of the vacuum inthe conduit with respect to time is greater than or equal to a constantvalue. If the rate of change is greater than or equal to the constantvalue, this indicates that the variation in the vacuum is a result of apost-occlusion surge.

It is preferred that the step of venting the conduit involves operatinga vent valve of the machine to vent the conduit. The vent valve may ventthe conduit for a predetermined period of time.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

In order that the invention may be more fully understood and put intopractice, an embodiment thereof will now be described with reference tothe accompanying illustrations, in which:

FIG. 1 illustrates a prior art peristaltic pump-based phaco-machine foruse in cataract eye surgery;

FIG. 2 illustrates a portion of the prior art phaco-machine depicted inFIG. 1 with the pump tube and vacuum sensor thereof represented by acompliant chamber;

FIG. 3 is a typical graph of the variation over time of the vacuum inthe compliant chamber of the prior art phaco-machine depicted in FIGS. 1and 2 immediately after an occlusion in the probe tip of the machine isremoved;

FIG. 4 is a typical graph of the variation over time of the flow offluid through the aspiration tube of the prior art phaco-machineillustrated in FIG. 1 immediately after an occlusion in the probe tip ofthe machine is removed;

FIG. 5 is a typical graph of the variation over time of the pressureinside the anterior chamber of an eye which is treated with the priorart phaco-machine illustrated in FIG. 1 immediately after an occlusionin the probe tip of the machine is removed;

FIG. 6 is a schematic block diagram of a post-occlusion surge detectorof a post-occlusion surge controller for the phaco-machine depicted inFIG. 1;

FIG. 7 is a schematic block diagram of a valve controller of thepost-occlusion surge controller for the phaco-machine depicted in FIG.1;

FIG. 8 is a graph of the variation over time of the voltage signaloutput by the vacuum sensor of the prior art phaco-machine depicted inFIG. 1 immediately after an occlusion in the probe tip of the machine isremoved;

FIG. 9 superimposes the graph depicted in FIG. 3 on a graph of thevariation over time of the vacuum sensed by the vacuum sensor of theprior art phaco-machine depicted in FIG. 1 immediately after anocclusion in the probe tip of the machine is removed when the machine isequipped with the post-occlusion surge controller;

FIG. 10 superimposes the graph depicted in FIG. 9 with a graph of thevariation over time of the pressure inside the anterior chamber of aneye which is treated with the prior art phaco-machine depicted in FIG. 1immediately after an occlusion in the probe tip of the machine has beenremoved when the machine is equipped with the post-occlusion surgecontroller;

FIG. 11 is a schematic block diagram of another post-occlusion surgecontroller;

FIG. 12 is a graph of the variation over time of the vacuum sensed bythe vacuum sensor of the prior art phaco-machine depicted in FIG. 1immediately after the removal of an occlusion in the probe tip of themachine when the machine is equipped with the post-occlusion surgecontroller depicted in FIG. 11;

FIG. 13 is a graph of the trigger signal which is output by thepost-occlusion surge detector of the post-occlusion surge controllerdepicted in FIG. 11;

FIG. 14 is a graph of the signal which is output by the vent valvedriver of the post-occlusion surge controller depicted in FIG. 11;

FIG. 15 is a graph which depicts the timing of the operation of the ventvalve of the prior art phaco-machine depicted in FIG. 1 when the machineincludes the post-occlusion surge controller depicted in FIG. 11;

FIG. 16 is a graph of the variation over time of the pressure inside theanterior chamber of an eye which is treated with the prior artphaco-machine illustrated in FIG. 1 immediately after the removal of anocclusion in the probe tip of the machine when the machine is equippedwith the post-occlusion surge controller depicted in FIG. 11;

FIG. 17 superimposes the graphs depicted in FIGS. 3 and 4 with thegraphs depicted in FIGS. 12, 15, and 16;

FIG. 18 is a schematic circuit diagram of the vent valve controllerdepicted in FIG. 7;

FIG. 19 is a schematic circuit diagram of the timer of the vent valvecontroller depicted in FIG. 7; and

FIG. 20 is a schematic circuit diagram of the post-occlusion surgedetector depicted in FIG. 6.

DETAILED DESCRIPTION OF THE ILLUSTRATIONS

The prior art phaco-machine 30 depicted in FIG. 1 can be modified toinclude a post-occlusion surge controller which includes apost-occlusion surge detector 60 which is depicted in FIG. 6, and avalve controller 61 which is depicted in FIG. 7.

The post-occlusion surge detector 60 includes a vacuum sensor input 62for connecting the detector 60 to the output of the vacuum sensor 48 ofthe phaco-machine 30 so that the electrical signal which is output bythe sensor 48 can be monitored and processed by the detector 60. Theelectrical signal which is output by the sensor 48 is a positive voltagewhich is proportional to the vacuum in the interconnected compliantcomponents of the machine 30 which is sensed by the sensor 48. Theoutput of the vacuum sensor 48 may, for example, be 10V/500 mmHg vacuum.

The detector 60 may include, for example, an operational amplifierconfigured as a differentiation amplifier, or a microcontroller. Thedetector 60 is configured to differentiate the electrical output of thesensor 48 with respect to time and to compare the differentiated outputwith a positive predetermined constant value so as to determine whetherthe negative of the rate of change with respect to time of the voltageoutput by the vacuum sensor 48 is greater than or equal to a positivepredetermined constant value. This can be expressed mathematically inthe form: ${{- \frac{\mathbb{d}V}{\mathbb{d}t}} \geq K},$where: V is the voltage output by the sensor 48 expressed in volts, t isthe time in seconds, and K is the positive predetermined constant valuehaving the units volts/second. This is proportional to directlydifferentiating the pressure sensed by the sensor 48 with respect totime, taking the negative of the differential, and then determiningwhether or not the result is greater than or equal to a positivepredetermined constant value of variation of pressure with respect totime, or: ${{- \frac{\mathbb{d}P}{\mathbb{d}t}} \geq X},$where: P is the pressure sensed by the sensor 48 expressed as mmHgvacuum (and is a negative value), t is the time in seconds, and X is thepositive predetermined constant value having the units mmHg/second (andis a positive value). X may, for example, be 1000 mmHg/second. The valueof X may be adjusted between 100 to 5000 mmHg/second to alter thesensitivity of the detector component 60. The value of X may bedisplayed on a control panel of the phaco-machine 30 and may be adjustedto the sensitivity that suits the preference of the surgeon who uses themachine 30.

If the negative of the differentiated output of the sensor 48 is greaterthan or equal to the positive predetermined constant value, a triggersignal 63 is output from a trigger signal output 64 of the detector 60to an input of the valve controller 61 as depicted in FIGS. 6 and 7. Thetrigger signal 63 is an inverted step function in which the output ofthe detector 60 changes abruptly from +10V to 0V. The trigger signal 63is output less than 1 millisecond after the detector 60 detects that therate of change of the vacuum sensor output voltage is greater than orequal to the value of K. The detector 60 detects this shortly after anocclusion in the tip of the probe 31 of the phaco-machine 30 breaks freebecause the vacuum inside the aspiration tube 41 of the machine 30 isfalling very rapidly at this stage but more slowly at other times duringoperation of the machine 30. This is depicted in FIG. 8 where it can beseen that the positive voltage output of the sensor 48 which isproportional to the vacuum inside the aspiration tube 41 decreasesrapidly after the occlusion breaks free such that the negative of therate of change of the voltage at the start of the illustrated waveformexceeds or is equal to the positive predetermined constant value. Theportion of the voltage waveform depicted in FIG. 8 which is below 0V isrepresented by a dotted line because the vacuum sensor 48 is only ableto output a positive voltage.

The detector 60 includes an input 98 for disabling the operation of thedetector 60 for experimental purposes such as for making experimentalrecordings of the reduced performance of the machine 30 when thedetector 60 (and, therefore, the post-occlusion surge controller) isdisabled. The detector 60 has an input 65 for enabling the detector 60to operate only if the machine 30 is being operated in a high vacuummode where the predetermined maximum allowable vacuum inside theaspiration tube 41 and other compliant components has been reached.Moreover, the detector 60 has an input 67 for enabling the detector 60to operate only when the vacuum inside the aspiration tube 41 and othercompliant components has reached 70% of the predetermined maximumallowable vacuum, or any other preset value.

The valve controller 61 illustrated in FIG. 7 includes a timer 70 whoseinput is connected to the output 64 of the post-occlusion surge detector60, and which outputs an ON vent valve control signal 71 to a vent valvedriver 72 and a high voltage pulse generator 73 for a predeterminedperiod of time immediately after receiving a trigger signal 63 from thedetector 60. The valve controller 61 also includes a vent valvepre-energiser 74. The vent valve driver 72 and the high voltage pulsegenerator 73 energise a solenoid of the vent pinch valve 50 of thephaco-machine 30 while receiving the vent valve control signal 71 fromthe timer 70 so that the vent pinch valve 50 opens and thereby vents theinside of the aspiration tube 41 to fluid or air which has a higherpressure than that inside the tube 41. Venting the aspiration tube 41 inthis manner causes the vacuum inside the tube 41 and other compliantcomponents to rapidly decrease and reduces both the amplitude andduration of the post-occlusion surge. Once the timer 70 times out, thevent valve driver 72 ceases energising the solenoid of the vent pinchvalve 50 so that the valve 50 pinches the venting tube 49 of thephaco-machine 30 to prevent further venting of the aspiration tube 41through the venting tube 49. The machine 30 is then able to resumenormal operation. Upon receiving the vent valve control signal 71, thehigh voltage pulse generator 73 outputs a high voltage signal 75 whichtimes-out prior to the vent valve control signal 71 in all cases. Thepre-energiser 74 switches off on account of the vacuum in the aspirationtube 41 falling to a value which is lower than the value which enablesthe pre-energiser 74.

The high voltage pulse generator 73 can be regarded as a current sourcedrive to the solenoid of the vent pinch valve 50 which functions torapidly establish an opening current in the solenoid coil of the ventpinch valve 50. The coil is inductive, and therefore opposes a rapidrate of change in current. A rapid increase in the current can beachieved with either the application of a high voltage pulse, whichattempts to generate a rapid increase in current, or a current sourceequivalent circuit which attempts to apply a constant current throughthe solenoid, and also therefore generates a high voltage pulse in theprocess of doing so. The net effect of either a high voltage pulse, or acurrent source drive, is equivalent.

When the solenoid of the vent pinch valve 50 is energised by the driver72 or high voltage pulse generator 73 it is important that the valve 50opens as quickly as possible to minimise the delay in arresting thepost-occlusion surge and to reduce the possibility of damaging the eye53 which is being treated with the phaco-machine 30. The delay inopening the vent pinch valve 50 can be reduced if the vent pinch valve50 is a normally closed electromechanical pinch valve which ismaintained in the closed position by a spring when the solenoid of thevalve 50 is not energised. This enables the solenoid of the valve 50 tobe pre-energised prior to being opened such that the valve 50 is on theverge of opening. This reduces the electromechanical delay in openingthe valve 50. It has been found that pre-energising the solenoid of thevalve 50 in this manner results in valve opening times of 30 to 40milliseconds being achieved as opposed to valve opening times of over100 milliseconds when the valve 50 is not pre-energised. Driving thevalve 50 with a high voltage pulse further reduces the delay to 20milliseconds.

The vent valve 50 is pre-energised by the pre-energiser 74. The outputof the pre-energiser 74 is connected to the solenoid of the vent pinchvalve 50 by the driver 72 and, when enabled, the pre-energiser 74applies a pre-energising voltage across the solenoid so that the ventpinch valve 50 is on the verge of opening. The pre-energiser 74 includesan input 76 for disabling its operation when the machine 30 is used in alow vacuum mode where the predetermined maximum allowable vacuum insidethe aspiration tube 41 is set to a relatively low level. Thepre-energiser 74 also has an input 77 for enabling its operation whenthe vacuum inside the aspiration tube 41 exceeds 70% of thepredetermined maximum allowable vacuum level or some other preset levelof measured aspiration tube vacuum. The pre-energiser 74 may also have aswitch for disabling its operation for purposes such as makingexperimental recordings.

FIG. 9 depicts a graph 80 of the variation over time of the vacuuminside the aspiration tube 41 of the machine 30 fitted with thepost-occlusion surge controller which includes the detector 60 and thevalve controller 61 immediately after an occlusion in the tip of theneedle 33 of the machine 30 is removed. Around 40 milliseconds after theocclusion is removed (i.e., around 40 milliseconds after t=0 seconds),the valve controller 61 has opened the valve 50 after receiving atrigger signal 63 from the surge detector 60 so that the rapidly openedvent valve 50 causes the vacuum inside the aspiration tube 41 to rapidlydecrease beyond zero to the eye pressure due to bottle height, pgh,which in turn reduces the amplitude and duration of the post-occlusionsurge. The oscillations in the graph 80 of the vacuum are a result oflow resistance in the pathway to the vent valve 50. In a system ofdamped simple harmonic motion, reducing the resistance encouragesoscillations. Note that the positive pressure values of the graph 80depicted in FIG. 9 would not be sensed by the sensor 48 because thesensor 48 can only sense vacuum and not positive pressure. Forcomparative purposes, the graph depicted in FIG. 3 is superimposed onthe graph 80 and is represented by a dotted line.

The variation over time of the pressure inside the anterior chamber ofan eye 53 treated with the post-occlusion surge controller equippedversion of the machine 30 is depicted in FIG. 10 by the waveform 81.Waveform 81 depicts the variation of the eye pressure immediately afteran occlusion in the probe tip of the machine 30 is removed. Incomparison to the eye pressure graph depicted in FIG. 5, the peak of thedrop in eye pressure depicted by the waveform 81 has been significantlyattenuated. Moreover, the duration of the waveform 81 has beensignificantly reduced in comparison to the duration of the waveformdepicted in FIG. 5. The attenuation in the peak drop in eye pressure andthe reduced duration of the drop in eye pressure correspond to areduction in the post-occlusion surge. Waveform 81 is superimposed overa graph of the variation over time of the vacuum in the aspiration tube41 of the same machine 30 over the same period of time when the machine30 includes the post-occlusion surge controller. The portions of thegraph of the variation over time of the vacuum in the aspiration tube 41which are above zero pressure are depicted by dotted lines becausevacuum levels above zero (i.e., positive pressures) are not sensed bythe vacuum sensor 48 which only outputs a positive voltage for a vacuum.

A schematic block diagram of a different post-occlusion surge controller90 is illustrated in FIG. 11. For convenience, features of thecontroller 90 which correspond to features of the previously describedpost-occlusion surge controller are referenced using the same referencenumbers.

Post-occlusion surge controller 90 is identical to the previouslydescribed post-occlusion surge controller except that the high voltagepulse generator 73 and pre-energiser 74 of the controller 90 are onlyenabled when the measured vacuum in the aspiration tube 41 is greaterthan 150 mmHg. The high voltage pulse generator 73 and the pre-energiser74 respectively include an input 91 and an input 92 for receiving anenable signal which enables the generator 73 and the pre-energiser 74.

At the beginning of the post-occlusion surge, fluid enters the probe endof the aspiration tube 41, and the wall of the aspiration tube 41 beginsto expand to its original geometry, prior to compression by atmosphericpressure. The expansion of the aspiration tube 41 progresses along thelength of the tube 41 (which is typically 2 metres long) from the probetowards the pump 40 at 360 kilometres per hour. When this reaches thevacuum sensor 48 there is an abrupt drop in vacuum. This assists thedetector circuit 60 to detect the start of the post-occlusion surge.

Moreover, the pre-energiser 74 of the post-occlusion surge controller 90does not have a disable switch and does not include separate inputs forenabling it when the vacuum is greater than 70% of the maximum allowablevacuum, and for disabling it when the machine 30 is being used in a lowvacuum mode.

The valve driver 72, vent valve 50, and pre-energiser 74 of thecontroller 90 are powered by a 12V supply voltage, while the generator73 is powered by a 40V supply voltage. Also, the vent valve controlsignal 71 which is output by the timer 70 has a reduced duration of 50milliseconds to reduce the time that the valve 50 is open which reducesoscillations of the vacuum in the aspiration tube 41 of the machine 30from those depicted in FIG. 9 to those depicted in FIG. 12.

The timer 70 includes an input 93 for controlling the standardfunctioning of the timer 70. Additional information in relation to theinput 93 is provided further on in relation to FIG. 18.

FIG. 11 depicts a high voltage pulse timing waveform 95 which isgenerated by the high voltage generator 73 coincident with the risingedge of the vent valve control signal 71, the timing relationshipbetween the waveform 95 and the signal 71 is also depicted.

FIG. 11 also depicts an output signal 96 which is output by the vacuumsensor 48 during the post-occlusion surge.

The timing of the trigger signal output by the detector 60, the outputsignal 71 of the timer 70, and the opening time of the vent valve 50relative to the waveform depicted in FIG. 12, is provided in FIGS. 13 to15. Due to the compliance of the aspiration tube 41, there is a 20millisecond delay, t₁, between the start of the surge in the eye and aresponse by the vacuum sensor 48 of the machine 30. The 20 milliseconddelay, t₁, adds to the 20 millisecond delay, t₃, to deploy the valve 50.The valve 50 therefore mechanically deploys approximately 40milliseconds after the actual surge in the eye starts. This delay isshort enough to allow the surge neutralisation to be effective asdepicted in FIG. 16. There is also a short delay, t₂, which isattributable to the detector 60 but which is insignificant.

Referring to FIG. 17, the graphs depicted in FIGS. 3 and 4 arerepresented by dotted lines and are superimposed on the graphs depictedin FIGS. 12, 15, and 16. The representation in FIG. 17 of the graphsdepicted in FIGS. 12, 15, and 16, are an actual recording of theperformance of the machine 30 when equipped with the controller 90.

FIG. 18 is a schematic circuit diagram of the valve controller 61 whichbelongs to the post-occlusion surge controller 90. The timer 70 includesan input 97 which is connected to the output 64 of the post-occlusionsurge detector 60, and an input 93 for controlling the timer 70 so thatthe valve controller 61 is also able to control the vent pinch valve 50to vent the aspiration tube 41 at times other than when a post-occlusionsurge is detected by the detector 60. The timer 70 also includes aninput 98 for disabling the timer 70.

The output of the timer 70 from which the vent valve control signal 71is output is connected to a first input of an AND logic gate 99 and tothe base of a Darlington transistor T1 via a 5.1 kΩ resistor R1. Anoverride input 100 is also connected to the base of the Darlingtontransistor T1 via a 5.1 kΩ resistor R2.

An input 101 for enabling the high voltage pulse generator 73 and thevent valve pre-energiser 74 is connected to an input of an AND logicgate 102. Another input of the AND gate 102 is connected to the outputof an AND logic gate 103. An input of the AND logic gate 103 isconnected to the output of an AND logic gate 104. Gate 104 is connectedto a first low level disable input 105 and a second low level disableinput 106, while an input of the gate 103 which is not connected to theoutput of the gate 104 is connected to a third low level disable input107. The output of the gate 102 is connected to an input of the gate 99.The output of the gate 102 is also connected to the base of a Darlingtontransistor T2 via a 10 kΩ resistor R3. The base of the transistor T2 isalso connected to ground via a 47 kΩ resistor R4. The output of the gate102 is also connected to input 65 of the detector 60. The output of thegate 102 is high when the high voltage pulse generator 73 and the ventvalve pre-energiser 74 are enabled and low when the high voltage pulsegenerator 73 and the vent valve pre-energiser 74 are disabled.

The output of the gate 99 is connected to the base of a transistor T3via a 10 kΩ resistor R5. The emitter of the transistor T3 is connectedto ground, while the collector of the transistor T3 is connected to thebase of a Darlington transistor T4 via a 4.7 kΩ resistor R6. The base ofthe transistor T4 is connected to the emitter thereof via a 47 kΩresistor R7.

The emitter of the transistor T1 is connected to ground. The collectorof the transistor T1 is connected to the collector of the transistor T4via a diode D1. A normally closed 12V vent valve solenoid 108 isconnected across the diode D1. The collector of the transistor T1 isalso connected to the collector of the transistor T2 via a 2 Watt 39Ωresistor R8.

The emitter of the transistor T4 is connected to ground via a 5600 μFcapacitor C1. A positive terminal of the capacitor C1 is connected to a+40V power supply via a 2 Watt 470Ω resistor R9. The positive terminalof the capacitor C1 is also connected to a +12V power supply via a diodeD2. The +12V power supply is also connected to the collector of thetransistor T4 via a diode D3. The high voltage pulse 95 is output fromthe collector of the transistor T4.

The 0V reference outputs of the +40V and +12V power supplies areconnected to ground.

The relative timing of the trigger signal 63, vent valve control signal71 and the high voltage pulse 95 are also depicted in FIG. 18.

During standard vent valve deployment, the vent valve solenoid 108 isactivated via input 93 to the timer 70, the output of which drives theDarlington transistor T1. When T1 is conducting, current flows from the12V supply, via diode D3, through the solenoid coil 108 and transistorT1 to ground.

Diode D1 absorbs the EMF (voltage spike) generated by the solenoid 108when T1 ceases to conduct at the end of the timing cycle when the fieldin the solenoid 108 collapses. This protects T4, T1 and T2 from beingdamaged. This completes the circuit, and the valve 50 of the machine 30opens for the duration specified by the valve control signal 71 which isoutput by the timer 70.

However, in this usual mode, depending on the particular solenoid 108,there is a delay of 80 to 150 milliseconds between the time that thetimer 70 gives the command to open before the actual valve 50 opens,because it takes time to establish the opening current in the solenoidcoil 108 and time to move the mass of the armature or moving core of thesolenoid 108. In addition, once the valve 50 opens and the infusionfluid 37 starts to flow there is a further delay of around 40milliseconds before the effects of venting are realised in the anteriorchamber of the eye 53. In usual operation this delay is not a concern.However, if the valve 50 is to be used as a “post-occlusion surgeneutralisation device”, it must have accelerated operation, as a typicalsurge has already peaked at 200 milliseconds after it begins.

The valve controller 61 is also capable of controlling the vent valve 50when the vent valve solenoid 108 is of the normally closed type (i.e.closed with a spring) and opened with the application of electricaldrive to the solenoid 108.

Post-occlusion surges occur in high vacuum modes duringphaco-emulsification, typically over 100 to 150 mmHg, and in some modesof phaco-machine use, for example low vacuum mode orirrigation/aspiration (IA) mode surges are not as troublesome and thefunction of surge neutralisation is not needed. Therefore, the ventcontroller circuit 61 includes inputs to enable or disable thespecialised operations.

As mentioned previously, the vent controller circuit 61 includes ANDlogic gates 99, 102, 103, and 104 which are standard dual input logicAND gates where both inputs need to be high to enable or give a highoutput. For the output of gate 102 to be high, all inputs, 101, 105,106, and 107, must be high. Taking any of those inputs low takes theoutput of gate 102 low.

Input 101 is high only when the vacuum sensed in the aspiration tube 41is over 150 mmHg (or any other level specified), and surges areanticipated, and is otherwise low to disable the function. The otherinputs 105, 106, 107 can be taken low to disable the function at anytime. For example, input 105 can be taken low in IA mode or 106 takenlow in low vacuum mode and 107 could be used to deactivate thespecialised operation on command.

When the output of gate 102 is high, this is the enable signal whichenables the post-inclusion surge controller 90 in anticipation of apost-occlusion surge, and the NPN Darlington transistor T2 is able toconduct. A current, determined by the value of R8, flows from the 12Vpower supply, via D3, through solenoid 108, and then via R8 and T2 tocomplete the circuit. The value of R8 is selected so the current flowingthrough the solenoid 108 is close to but below the current required toopen the vent valve 50. This reduces the time it takes to increase thecurrent to the value which will cause the vent valve 50 to open. This isthe pre-drive current, applied in anticipation of the need for a rapidvalve deployment. The enable signal which is output by the gate 102 isalso used to enable the surge detector 60 that generates the triggersignal 63 that drives the timer 70.

Pre-drive current is present therefore prior to a post-occlusion surgeand when the surge is detected by the detector 60 (i.e. is a rapid rateof change of vacuum in the aspiration tube 41) the trigger signal 63 isgenerated and fed to input 97 of the timer 70. This triggers the timer70 so that the output of the timer 70 goes high for the opening period.At this point, a number of things occur.

One thing which occurs is that T1 conducts, and the current flowingthrough the solenoid coil 108 starts to increase above the pre-drivevalue. The output of the timer 70 is passed via gate 99 to NPNtransistor T3 which conducts, turning on PNP Darlington transistor T4.

Also, T4 is connected to C1, a capacitor charged to the potential of the+40V power supply, via a charging resistor R9 so that approximately 4.5Joules of energy is stored in the capacitor C1. Moreover, diode D2 isreverse biased and is not conducting. At the moment T4 conducts, thecapacitor C1 is switched to the uppermost terminal of the vent valvesolenoid 108, and the lower terminal of the vent valve solenoid 108 isat ground potential as T1 is conducting also during the timing period.Capacitor C1, via transistor T4, immediately applies the +40V to thesolenoid 108 and this rapidly increases the current to the openingvalue.

At the time T4 is conducting (i.e. during the time that the timer 70 ishigh), the uppermost terminal of the solenoid 108 spikes to +40V anddiode D3 is reverse biased, decoupling the standard +12V drive from theupper terminal of the solenoid 108. The width of the high voltage pulse95 is shorter than the period of the vent valve control signal 71, anddecays away as capacitor C1 rapidly discharges into the solenoid 108.This prevents the solenoid 108 from overheating from excessive drive.Only an initial impulse is required for the rapid opening. The diode D2prevents capacitor C1 discharging below 11.3V. Therefore, after theinitial rapid pulse occurs at the opening time, the solenoid currentreturns to its standard value.

After the timing period T3, T4 and T1 turn off. Due to thepost-inclusion surge controller 90 having controlled the vent valve 50to vent the aspiration tube 41 of the machine 30, the vacuum in theaspiration tube 41 is very low or positive from the pressure of theinfusion fluid 37 in the bottle 36, and the input 101 falls low becausethe vacuum in the aspiration tube 41 is below 150 mmHg. T2 also turnsoff and the pre-drive current is now zero. With no current flowingthrough the solenoid coil 108, the spring of the vent valve 50 causesthe valve 50 to close. At this time, C1 also recharges to the 40V supplypotential via R9. When the vacuum in the aspiration tube 41 later climbsabove 150 mmHg, the pre-drive current returns and the system is “armed”again ready to neutralise another post-inclusion surge.

FIG. 19 is a schematic circuit diagram of the timer 70 of the valvecontroller 61 which belongs to the post-occlusion surge controller 90.

Timer 70 includes a 555 timer integrated circuit IC1 which includes pinsP1, P2, P3, P4, P5, P6, P7, and P8. Pin P1 is connected to ground, andpin P5 is connected to ground via a 0.01 μF capacitor C2. Pins P7 and P6are connected to ground via a 1 μF capacitor C3, and to pin P8 via a 47kΩ resistor R10. Pin P3 is connected to resistor R1 and gate 99 whichare depicted in FIG. 18. Pin P4 of the timer IC1 is connected to input98 which is depicted in FIG. 18.

A diode D4 and a 100 kΩ resistor R11 are connected to each other inparallel and across pins P2 and P8. The vent valve control signal 71 isoutput by the timer IC1 on pin P3. The duration of the signal 71 is 51.7milliseconds and is calculated by multiplying the product of thecapacitor C3 and the resistor R10 by 1.1.

Pin P8 is connected to a +10V power supply and to ground via a 10 μFcapacitor C4. The 0V reference output of the +10V power supply isconnected to ground.

Pin P2 of the IC1 is connected to a diode D5 and a diode D6 via a 0.1 μFcapacitor C5. Pin P8 is connected to the diodes D5 and D6 via a 100 kΩresistor R12. Diode D5 is connected to input 93 of the timer 70, whilediode D6 is connected to input 97 of the timer 70.

Timer 70 can be disabled, for example in the machine setup mode by theinput 98. The vent valve 50 can be opened at any time, for example inthe machine setup mode to assist insertion of the aspiration tube 41into the head of the valve 50, by the override input 100 depicted inFIG. 18. Timer 70 is a standard circuit. Timer 70 may be implemented ineither software or hardware.

FIG. 20 is a schematic circuit diagram of the post-occlusion surgedetector 60 which belongs to the post-occlusion surge controller 90.

Vacuum sensor 48 of the phaco-machine 30 includes a sensor component 109whose input is connected to the lumen of the aspiration tube 41 of themachine 30, and an amplifier component 110 which amplifies theelectrical signal which is output by the sensor component 109. Theoutput of the amplifier component 110 is able to vary between 0 to 10Vwhich corresponds to a vacuum variation in the lumen of the aspirationtube 41 of 0 to −500 mmHg. Thus a 50 mmHg variation in vacuumcorresponds to a 1V variation in the output of the amplifier component110.

The output of the amplifier component 110 of the vacuum sensor 48 isconnected to the negative input of an operational amplifier IC2 via a 1kΩ resistor and 1 μF capacitor C6 which are connected in series to eachother. The negative and positive inputs of IC2 are connected to eachother by a pair of parallel diodes D7, D8. The positive input of IC2 isalso connected to ground. The negative input and output of IC2 areconnected to each other via a resistor R14 which is typically a 300 kΩresistor. The output of IC2 is connected to the negative input of anoperational amplifier IC3 and to the collector of a transistor T5 via a5.1 kΩ resistor R15. IC2 is powered by a +10V power supply.

The base of the transistor T5 is connected to a +10V power supply via a9.1 kΩ resistor R16, and to the collector of a transistor T6. Theemitter of transistor T6 is connected to ground, and the base oftransistor T6 is connected to an enable input 65 of the controller 61via a 20 kΩ resistor R17.

A positive input of the operational amplifier IC3 is connected to a +6Vreference voltage. The output of IC3 is connected to the input 97 of thevalve controller 61. IC3 is powered by a +10V power supply.

Operational amplifier IC2 is configured as a differentiator and is usedto monitor the output from the amplifier component 110 of the vacuumsensor 48. The output of IC2 is fed into the operational amplifier IC3which is configured as a comparator and which is referenced to the fixed+6V reference voltage. The trigger signal 63 is generated by IC3 whenthe negative rate of change of the voltage output of the amplifiercomponent 110 is greater than or equal to the +6V reference divided bythe product of resistor R14 and capacitor C6. This corresponds to thevoltage output by the operational amplifier IC2 being greater than orequal to the +6V reference voltage. In a worked example with R14 havinga value of 300 kΩ and C6 having a value of 1 μF, dividing the +6Vreference voltage by the product of the resistor R14 and the capacitorC6 gives 20V/second (50 mmHg corresponds to 1V from the amplifiercomponent 110). This corresponds to a rate of change of vacuum of 1000mmHg/second, to generate the trigger signal 63. The threshold for thetrigger signal 63 as determined by the reference voltage and product ofC6 and R14 sets the “sensitivity” of the detector 60 and can be adjustedto any value, for example, between 100 and 5000 mmHg/second. Significantpost-occlusion surges have higher rates of change of vacuum associatedwith them, so the sensitivity can be set so that the venting does notexcessively interrupt the course of the cataract extraction. Diodes D7and D8 allow for rapid recharging of differentiator capacitor C6. T5 andT6 are used to disable the detector when the output of gate 102 is low,or in the disabled state. The surge detector 60 may be implemented inhardware or in software.

The above techniques shorten the opening time of the vent valve to 20milliseconds after the trigger signal 63 is presented. The triggersignal 63 is generated 20 milliseconds after the surge begins in the eye53, so there is an overall latency of 40 milliseconds. Another 40milliseconds delay is encountered prior to any measurable effect of theventing at the machine 30, near the vent valve 50, reducing the surge inthe eye 53. The deployment of the vent valve 50 therefore occurssignificantly sooner than when the unaltered surge would have otherwisepeaked at around 200 milliseconds. The result is a post-occlusion surgeof significantly lower amplitude and duration. This reduced surge hasapproximately one-third of the area below the curve of pressure versustime compared to any existing machine.

The vent valve solenoid 108 is preferably constructed with the lowestpossible mass armature or moving core so as to reduce the inertia of thevent valve 50 by as much as possible.

Plain transistors, Darlington transistors, power MOSFETS, or IGBT's orsimilar can be used to implement the circuit configuration.

The present invention allows for early detection and arrest of thepost-occlusion surge such that both the amplitude and duration of thesurge are reduced. This enables a phaco-machine which is equipped withthe invention to be used with high maximum vacuums whilst the amplitudeand duration of any post-occlusion surges which may occur remain withinacceptable limits.

It will be appreciated by those skilled in the art that variations andmodifications to the invention described herein will be apparent withoutdeparting from the spirit and scope thereof. The variations andmodifications as would be apparent to persons skilled in the art aredeemed to fall within the broad scope and ambit of the invention asherein set forth.

1. A post-occlusion surge controller for a phacoemulsification machine,wherein the controller is adapted to detect a post-occlusion surge in anaspiration conduit of the machine, and to cause the conduit to be ventedin response to detecting the surge.
 2. The post-occlusion surgecontroller of claim 1, wherein the controller is adapted to detect theonset of the surge, and to cause the conduit to be vented in response todetecting the onset of the surge.
 3. The post-occlusion surge controllerof claim 2, wherein the controller includes a detector for detecting theonset of the surge, and a valve controller for controlling a vent valveof the machine in response to the detector detecting the onset of thesurge.
 4. The post-occlusion surge controller of claim 3, wherein thedetector includes a differentiator for differentiating the output of avacuum sensor of the machine, and a comparator for comparing the outputof the differentiator with a reference value and for outputting atrigger signal depending upon the outcome of the comparison.
 5. Thepost-occlusion surge controller of claim 4, wherein the valve controllerincludes a timer for outputting a vent valve control signal in responseto receiving the trigger signal, and a vent valve driver for driving thevent valve to vent the aspiration conduit in response to the vent valvecontrol signal.
 6. The post-occlusion surge controller of claim 5,wherein the valve controller includes a high voltage pulse generator foroutputting a high voltage pulse signal to a solenoid of the vent valvein response to the vent valve control signal.
 7. The post-occlusionsurge controller of claim 6, wherein the valve controller includes avent valve pre-energiser for pre-energising the solenoid.
 8. A method ofcontrolling a post-occlusion surge in an aspiration conduit of aphacoemulsification machine, the method comprising the steps of: (i)detecting the post-occlusion surge; and (ii) venting the conduit inresponse to detecting the surge.
 9. The method of claim 8, wherein thestep of detecting the surge involves detecting the onset of the surgeand the step of venting the conduit is done in response to detecting theonset of the surge.
 10. The method of claim 9, wherein the step ofdetecting the onset of the surge includes determining whether thenegative of the rate of change of the vacuum in the conduit with respectto time is greater than or equal to a constant value.
 11. The method ofclaim 8, wherein the step of venting the conduit involve operating avent valve of the machine to vent the conduit.
 12. The method of claim11, wherein the vent valve vents the conduit for a predetermined periodof time.